Silicone resins have been used for a number of purposes because of their thermal stability, dielectric properties, chemical stability, and resistance to atmospheric deterioration. For example, the papers, "Electrical Performance and Reaction Kinetics of Silicone Gels," by C. P. Wong, Journal of Materials Research, Vol. 5, No. 4, April 1990, pp. 795-800, and "Understanding the Use of Silicone Gels for Non-Hermetic Plastic Packaging," by C. P. Wong et al., IEEE Transactions on Components, Hybrids and Manufacturing Technology, Vol. 12, No. 4, December 1989, pp. 421-425, describe the use of silicone resins as encapsulates for electronic devices, particularly integrated circuits.
The patent of Wong, U.S. Pat. No. 4,888,226, granted Dec. 19, 1989, is directed to a silicone resin that is particularly suitable for wire bonded hybrid integrated circuits. A hybrid integrated circuit is one in which a semiconductor chip, usually a silicon chip, is connected to a bonding pad region of a circuit pattern on a ceramic substrate. The patent describes the need for an encapsulant that will protect delicate bonding wires interconnecting the chip with the bonding pad under varying conditions of temperature and humidity, and with high integrated circuit bias voltages. While polydimethylsiloxane is adequate for most purposes, such silicone resins tend to crystallize at extremely low temperatures, such as temperatures below about -35.degree. C.(-31.degree. F.). Such crystallization may break the delicate bonding wires and may crack the encapsulant to expose the electronic device to contaminants from the outside environment. There is therefore a continuing need for integrated circuit encapsulates that give a high degree of protection from outside contaminants, even under conditions of extreme cold.